The design of ophthalmic lenses intended to be mounted in a spectacle frame in order to correct the visual defects of a wearer is of particular importance in so far as whether this pair of spectacles will be acceptable or not depends to a large extent upon said design.
This design is in particular critical when it relates to progressive or multifocal lenses, and lenses intended to compensate for the astigmatism of the wearer.
As is known, the optical design of a pair of ophthalmic lenses for correcting cylindrical and spherical refractive defects of the two eyes of a wearer comprises:                a step of defining the cylindrical and spherical correction requirements of the wearer for various vision proximities, and        a step of determining cylindrical and spherical powers of said ophthalmic lenses at vision points of various proximities, depending on the previously defined cylindrical and spherical correction requirements of the wearer.        
The first step may be carried out by an ophthalmologist who delivers an optical prescription to the wearer, this prescription comprising for each proximity, for example for far vision, intermediate vision and/or near vision:                a sphere value in diopters for the correction of spherical ametropias, such as myopia or hypermetropia in far vision,        a cylindrical value with the datum of its modulus in diopters and the datum of its axis in degrees, this cylinder having the aim of correcting any astigmatism of the wearer at the various proximities.        
With such a differentiated prescription (right eye/left eye and far vision/near vision), the second step could in certain cases lead, without specific treatment, to disparate cylindrical and spherical powers, and thus to possible discomfort for the wearer.